In this disclosure the term virtual LAN (“VLAN”) means a data communication network which comprises a number of segments which are connected together by links which operate according to a networking protocol different from that of the network segments. For example, two segments of an ethernet network may be connected by way of a channel in a connection-based network. The channel may be, for example, a virtual circuit in an asynchronous transfer mode (ATM) network. Each of the network segments may be interfaced to the connection-based network by a bridge.
Data may be delivered between the segments in any of a wide number of ways. For example, where the segments comprise ethernet segments and the network which connects the segments comprises an ATM network then ethernet frames may be carried between the segments according to standards such as local area network emulation (“LANE”), multi-protocol over ATM (“MPOA”) or IP over ATM. Data may be carried on a path in a MPLS network. The particular format by which data is conveyed between network segments is not important to this invention.
IEEE standard 802.1Q provides a set of capabilities which permit media access control (MAC) bridges to define and manage networks in which multiple broadcast domains can co-exist on a single physical medium. This IEEE standard uses the term “VLAN” to describe such networks. In this disclosure the term VLAN is not used in the same sense as it is in IEEE 802.1Q (although this invention may be applied to networks which operate, or which include portions which operate, according to IEEE 802.1Q). IEEE standard 802.1D describes the operation of MAC bridges.
Various networking protocols permit priorities (sometimes called “user priorities”) to be assigned to data. Through the use of such protocols, data having different priority levels can be treated differently. For example, certain levels of Quality of Service (QoS) may be specified for each priority level. An example of a networking protocol which accommodates user priorities is the IEEE 802.1D standard which relates to ethernet networks. Annex H of IEEE standard 802.1D describes a way to map user priorities to service queues.
U.S. Pat. No. 6,175,569 discloses a method for extending QoS guarantees to stations on a token ring LAN. The method involves a LAN station originating a request for a connection through an ATM network to either a remote ATM station or a remote LAN station. A LAN/ATM interface device receives the request and attempts to establish the requested connection.
U.S. Pat. No. 5,978,378 discloses a method for identifying frames which relate to a VLAN and excluding such frames from ports not associated with the VLAN.
There is a need for ways to accommodate user priorities in VLANs.